Magnetic transducer



Nov. 17, 1964 K. R. ELDREDGE 3,157,743

MAGNETIC TRANSDUCER Filed March 24, 1961 INVENTOR.

KENNETH R. ELDREDGE .4 TTOR/VE X United States Patent "ice 3,157,748 MAGNETKC TRAWSDUQER Kenneth R. Eldredge, Palo Alto, Calif., assignor to General Electric Company, a corporation ofNew York Filed Mar. 24, 1961, Ser. No. 98,248 3 Claims. (iii. 179-1002) This invention relates to magnetic recording and more particularly to an improved multichannel magnetic trans ducer formed as a single unit of simple construction with close spacing of the channels or transducer elements thereof.

There are many instances in the magnetic recording art where it is desirable to record on and reproduce from a plurality of closely spaced parallel tracks. An example of the use of multiple-channel transducers is in the field of reading human languagesymbols which have been printed on documents with magnetic ink. In such magnetic symbol reading systems the symbols may be distinguished from one another by detecting and correlating the magnetic discontinuities ofthe Various portions of the printed symbol. In a known embodiment of a symbol reading system a wide, single element, reading transducer spans the vertical dimension of the symhole. and produces a waveshape characteristic of the symbol when a magnetized symbol is passed adjacent thereto. Such a system is feasible where only a limited number of symbols is used. However, expansion of the system to include a greater number of symbols requires that a greater number'of distinguishing characteristics be recognized. It is therefore desirable to separately detect vertical portions of the symbols. By the use of the multi-channel transducer of the present invention individual narrow strips of a symbol may be examined and in this way the number of distinguishing characteristics is greatly increased. The number of different symbols which can be distinguished is therefore correspondingly increased.

To achieve reading of printed symbols of normal size with a multichannel transducer, it is clear that the channels or transducer elements must be very closely spaced. Multichannel transducers of the prior art often comprise merely an aggregation of juxtaposed single transducers and close spacing thereof is difiicult if not impossible to achieve. Other 'prior art multichannel transducers which have been formed in a single unit require intricate parts and are complicated and expensive to produce. Also, prior art efforts to reduce cross-talk have mainly been directed to the use of various shielding materals and configurations between channels. Nonmagnetic shielding material is added to the structure at the expense of magnetic core material. In any case where very close spacing of the channels is required only very thin interchannel shields can be tolerated. It is therefore desirable to construct a multichannel transducer without the use of shielding material.

It is accordingly an object of the invention to provide an improved multichannel magnetic transducer.

Another object of the invention is to provide a multichannel transducer of simple design and low cost.

Another object of the invention is to reduce crosstalk among the channels of a multichannel transducer.

Another object of the invention is to construct a multichannel transducer without the use of shielding material. 1 7

Another object-of the invention is to form a plurality of recording and reproducing gaps in a single unit.

Another object of the invention is to provide accurate alignment of the gaps of a multigap transducer.

These and other objects of the invention are achieved by constructing a multichannel transducer from a pair of core members having adjacent ends formed in an appropriate shape to constitute pole tips for cooperation with a magnetic medium. A configuration of conductors is sandwiched between the core members so asto constitute a series of one-turn loops or coils whichare substantially separately responsive'to the passage of magnetized material adjacentrespective portions of the pole tips. To increase the signal to cross-talk ratio the reluctance of the cross-talk magnetic circuits may be inf creased and thereluctance of'the' signal magnetic cir-' cuits may be decreased by placing the conductive. configuration in grooves or depressions in the inner face of one of the core members so that the inner faces of the core members maybe in abutting relation. Thus the present invention provides a. multichannel transducer of simple construction, without intricate parts or interchannel shielding and in which the channels may be closely spaced.

The invention will be described in greater detail with reference to the accompanying drawings in which:

FIGURE 1 is a partly exploded perspective illustration of the preferred embodiment of the present multichannel transducer together with a schematic representation of transformer coupling to the channels'of the transducer;

FIGURE 2 is a perspective view of a first core member of the preferred embodiment of the invention; and

FIGURE 3 is an end view of the transducer illustrating the cooperation of the transducer with a magnetic mediurn.

Shown in FIG 1 is a partly exploded perspective illustration of the multichannel transducer according to the preferred embodiment of the invention. The transducer is formed of a first core member 10 and a second core member 11. While any suitable paramagnetic material may be used, the core members are preferably formed from a moldable sintered ferromagnetic material such, for example, as ferrite.

Adjacent ends of the core members 10 and 11 are formed to constitute a pair of respective pole tips 12 and 13. In the illustrated embodiment the pole tips are given a rounded shape for cooperation with a magnetic medium, illustrated as a medium 30 in FIG. 3.

As shown in FIG. 1 a conductive configuration is formed by a first strip 14, and a plurality of spaced strips 15(1)-l5(n) extending substantially perpendicular from strip 14 across the inner face of the core member 10.

The conductive strips are formed of a thin layer of nonmagnetic electrically conductive material such, for example, as copper. As may be seen in FIG. 1 the first strip 14 is positioned between and along the pole tips 12 and I3 and it therefore defines the transducing gap. Thus the thickness of the conductive strips is determined by the desired width of the transducing gap.

In the preferred embodiment of the invention the conductive strips are placed in grooves or depressions in the inner face of the core member 10. Therefore the core member 10 may first be formed as shown in FIG. 2 with grooves 24 and 25(1)25(n) thus resulting in a plurality of upstanding portions 26(1)-26(n) having their surfaces in a common plane. The grooves may then be filed with conductive material to form the conductive configuration asshown in FIG. 1. By this construction the surfaces of the upstanding portions 26(1)26(n) of the core member 10 may be placed in abutting relation with the inner surface of the core member 11 thus eliminating what would otherwise be an extended gap between the core members due to the conductive strips. Insulating material may be provided around the conductive strips in the event that a conductive core material is used.

From FIG. I it may be seen that adjacent pairs of the spaced strips 15(1)-15(n) together with the in- Patented Nov. 17, 1964 cluded or connecting portions of the strip 14 constitute a one-turn loop or coil around respectively circumscribed portions of the core members. For example, the strip 15(1) and 15(2) and the part of strip 14 designated 14(1) constitutes a loop around the upstanding portion 26 (1) of the core member 10. Thus when a magnetized portion of a magnetic medium passes adjacent the gap defined by the part 14(1) of strip 14 there will be a fiux linkage from the magnetized material through the loop formed of the strips 15(1), 14(1) and 15(2) via the adjacent portion of the pole tip 12, the upstanding portion 26(1) of the core member 10, the corresponding portion of core member 11, and the adjacent portion of pole tip 13. Thus each such loop is substantially separately responsive to the passage of magnetized material adjacent its portion of the transducing gap and, therefore, each loop defines a channel of the multichannel transducer.

The changing flux linkage through a conductive loop causes signals therein. As shown in FIG. 1, adjacent pairs of the strips 15(1)-15(21) are connected by leads, such as a lead 16, to the primary winding of a plurality of transformers, such as a transformer 17. The transformers match the relatively low impedance of the oneturn loops to the impedance of the utilization circuit (not shown) for effective transfer of the signals therebetween.

While the principles of the invention have been made clear in the illustrative embodiments, there will be obvious to those skilled in the art, many modifications in structure, arrangement, proportions, the elements, materials, and components, used in the practice of the invention, and otherwise, which are particularly adapted for specific environments and operating requirements, without departing from those principles. The appended claims are therefore intended to cover and embrace any such modifications within the limits only of the true spirit and scope of the invention.

What is claimed is:

1. A magnetic transducer for producing signals in response to movement of-magnetized portions of a magnetic medium adjacent thereto comprising; first and sec- 0nd juxtaposed core members formed of magnetic material and having abutting inner surfaces and portions adapted to form pole tips; a first groove in the inner surface along the pole tip of said first core member to form a signal transducing gap; a plurality of grooves joining said first groove and extending substantially perpendicular thereto across said inner surface of said first core member; and a nonmagnetic material having high electrical conductivity in said grooves.

2. A magnetic transducer comprising: a first core member having an edge adapted to form a first pole tip and having a substantially plane face, said face having a plurality of spaced parallel grooves disposed perpendicular to said edge, said face further having an additional groove parallel to and contiguous with said edge and communicating with said parallel grooves; a second core member of magnetic material having a substantially plane face abutting said plane face of said first core memher and having an edge adapted to form a second pole tip disposed opposite said first pole tip; and a nonmagnetic conductive material disposed in said grooves and substantially coextensive therewith.

3. A magnetic transducer comprising: a first magnetic core member having a plurality of separate spaced upstanding portions with the surfaces thereof in a common plane, and spaced from a given end of said first core member; a second magnetic core member having a plane surface abutting the surfaces of said upstanding portions of said first core member and an end conterminous with said given end; and a one-turn coil around each of said upstanding portions.

References Cited by the Examiner UNITED STATES PATENTS 2,536,272 l/Sl Friend l79-l00.2 2,647,167 7/53 Rettinger l79-100.2 2,866,013 12/58 Reis 179-100.2

IRVING L. SRAGOW, Primary Examiner.

DAVID G. REDINBAUGH, Examiner. 

1. A MAGNETIC TRANSDUCER FOR PRODUCING SIGNALS IN RESPONSE TO MOVEMENT OF MAGNETIZED PORTIONS OF A MAGNETIC MEDIUM ADJACENT THERETO COMPRISING; FIRST AND SECOND JUXTAPOSED CORE MEMBERS FORMED OF MAGNETIC MATERIAL AND HAVING ABUTTING INNER SURFACES AND PORTIONS ADAPTED TO FORM POLE TIPS; A FIRST GROOVE IN THE INNER SURFACE ALONG THE POLE TIP OF SAID FIRST CORE MEMBER TO FORM 